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accessibility text scale: global font multiplier synced to the desktop's text-scaling-factor
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New set_text_scale / text_scale process global (clamped [0.5, 3.0]) multiplied into every resolved font size — Canvas::resolve_font for explicit Lengths and the Physical branch of font_px (the Fluid branch routes through resolve_font) — so the whole tree's text follows the accessibility "large text" factor while geometry stays untouched, mirroring GNOME's text-scaling-factor semantics. Unit test covers fonts-scale-geometry-doesn't.
The run loop keeps the factor synced on its own: a watcher thread (event_loop/text_scale.rs) reads org.gnome.desktop.interface text-scaling-factor via gsettings get at startup and streams external changes from gsettings monitor into a calloop channel; on a change the loop stores the factor, invalidates the view caches and repaints main and overlays. Since fonts resolve at paint time nothing else needs rebuilding. Every ltk app tracks the settings slider live with zero app-side wiring, the same way GTK apps follow the key; missing gsettings degrades silently to a fixed 1.0. Embedders driving core::UiSurface (forge) call set_text_scale themselves — the multiplication only runs at widget font resolution, so raw Canvas::draw_text callers keep hand-computed sizes.
architecture.md documents the multiplier in the font-space paragraph and CHANGELOG gains the entry.
This commit is contained in:
Pedro M. de Echanove Pasquin
2026-08-02 22:50:19 +02:00
parent e343142347
commit d9652dce98
8 changed files with 155 additions and 5 deletions
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docs/architecture.md
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@@ -188,7 +188,7 @@ part of the `ltk::runtime` layer.
## Responsive sizing
Every size in a widget tree is a `Length`, resolved to concrete pixels at layout time against the surface. Two coordinate spaces matter. **Geometry** (widths, heights, paddings, gaps, box sizes) is computed in *physical* pixels — the layout root rect is `pw × ph` — so geometry `Length` values resolve against `Canvas::viewport_layout()` (physical). **Font sizes** are the exception: they resolve against `Canvas::viewport_logical()` (physical ÷ `dpi_scale`) and are multiplied by `dpi_scale` again at raster time, so a `vmin` font ends up as a fraction of the *physical* short side regardless of `dpi_scale`. Keep this split in mind when adding a widget: resolve a geometry constant with `Canvas::geom_px(n)` and a font constant with `Canvas::font_px(n)` — the two helpers hide the difference.
Every size in a widget tree is a `Length`, resolved to concrete pixels at layout time against the surface. Two coordinate spaces matter. **Geometry** (widths, heights, paddings, gaps, box sizes) is computed in *physical* pixels — the layout root rect is `pw × ph` — so geometry `Length` values resolve against `Canvas::viewport_layout()` (physical). **Font sizes** are the exception: they resolve against `Canvas::viewport_logical()` (physical ÷ `dpi_scale`) and are multiplied by `dpi_scale` again at raster time, so a `vmin` font ends up as a fraction of the *physical* short side regardless of `dpi_scale`. Keep this split in mind when adding a widget: resolve a geometry constant with `Canvas::geom_px(n)` and a font constant with `Canvas::font_px(n)` — the two helpers hide the difference. Font resolution additionally multiplies by the global accessibility `text_scale()` — the run loop keeps it synced to the desktop's `org.gnome.desktop.interface text-scaling-factor` GSettings key (initial `gsettings get` plus a `gsettings monitor` watcher thread) and repaints on change, so every ltk app follows the "large text" setting live; geometry never scales with it.
`ltk` offers two adaptation strategies, and both live in the same `Length` type so an app can mix them per value: